The invention relates to a process and device for monitoring a set value indicator of a drive motor of a motor vehicle which includes a brake system which can provide an actuating signal for the monitoring device and a motor output final control element which may reduce the drive output to a small value when the brake and the motor output set value indicator are actuated simultaneously.
Such a monitoring process is known from DE-OS No. 34 30 077; in this instance, a mechanical switch determines whether or not the accelerator pedal is located outside of the rest position. If a brake actuating signal is present and the accelerator pedal is simultaneously located outside of the rest position, it is assumed that the accelerator pedal is blocked and the motor output is therefore reduced. A further possibility which this system does not handle is described in Kolberg, G., "Electronic Motor Control for Motor Vehicles" in "Journal of Engine Technology", 4, 1985. In this case, when a high pedal value and a brake signal are present simultaneously it is concluded that there is a disturbance and the throttle flap is moved to a lower load position. However, at low outside temperatures the brake signal can last for seconds because of the viscous brake fluid, and starting is therefore made impossible.
Accordingly, it is an object of the present invention to prevent an erroneous blocking set value indication during a monitoring process of the type mentioned above and to prevent faulty drive motor control.
In keeping with these objects and others which will become more apparent hereinafter, the monitoring process for the motor drive output set value indicator includes the step of not reducing motor output or not keeping motor output reduced, when the first derivative of the set value of the motor output according to time is quantitatively greater than a threshold value and the brake actuation signal are simultaneously present. This means that the predetermined output set value is treated as a normal case of operation despite the brake actuation signal.
This process can further comprise reducing the drive motor output by reducing the air flow in the intake pipe or the fuel metering. In some embodiments the motor output can be reduced to or kept at the idling state corresponding to a lower partial load. The brake actuation signal can be obtained electronically preferably from the electric circuit for the brake lights.
Advantageously, however the drive motor output is not reduced only if the first derivative of the motor output set value according to time has a positive value.
The present inventin also includes a device for performing the monitoring process. This device includes a means for forming the first derivative according to time of the motor output set value, for detecting the magnitude of this value and combining it with the brake actuating signal, so that the drive motor output is not reduced when the motor output set value indicator is moved. The motor output set value indicator may be a potentiometer which is actuated by the driver via mechanical means and which transmits the set value as a voltage level. An analog and/or digital electronic unit may be provided to which the set value and the brake actuating signal are fed, which reduces or does not reduce motor output as necessary.